Polygonum Plant Growing & Care Guide for Gardeners

Article by Dean Ravenscroft, Ph.D. - Updated 26th Nov 2023

In this Gardener's HQ guide, we'll explore cultivating Polygonum plants in your garden, indoor spaces, and other settings.

Knotweed, Bistort, & Wiregrass: Cultivation & Garden Use

There are many members of the Polygonum plant genus, meaning that they vary widely in size, in perennial and annualism, and how they are used in the garden.

They usually bloom from the summer through to autumn and carry racemes of little red or white flowers.

The range in size and nature of Polygonum means that they can be used in many parts of the garden; however many members are aquatic and so can be used in boggy parts of the garden or in water features.

Some common names for Polygonum include Knotweed, Bistort, Russian Vine, Vietnamese Coriander, Smartweed and Prince's feather.

Commonly Grown Polygonum Species

Polygonum amphibium stipulaceum

Polygonum amphibium stipulaceum - Water Knotweed by Gmayfield10; creative commons.

Polygonum aviculare

Polygonum aviculare - Common Knotgrass by Matt Lavin; creative commons.

Polygonum multiflorum

Polygonum multiflorum (Tuber fleeceflower / Chinese climbing knotweed / He shou wu), photograph by 阿橋 HQ; CC.

Polygonum cuspidatum

Polygonum cuspidatum (Japanese knotweed / Asian knotweed), picture by Matt Lavin; CC.

How to Grow Polygonum Plants Such as Knotweed in the Garden

If growing outdoors from the off then it is best to sow Knotweed and other Polygonum species outside just after the last frost of spring; once sown lightly cover the Knotweed seeds with topsoil.

The plants prefer to grow in a partially shaded part of the garden and like to have a moist soil of pH 6 to 7.5.

Even though the soil should be moist it is important that Knotweed grows in areas of good drainage.

If starting Polygonum indoors then do so about three weeks before you expect the last frost.

The seeds can take anything from 3 to 8 weeks to germinate at a temperature of 21 to 24 degrees centigrade (70 to 75°F).

Once ready, transplant the seedlings at a spacing of 20 to 30 cm (8 to 12 inches) for small Polygonum species; 30 to 60 cm (12 to 24 inches) for medium size; or 70 cm to 1.2 m (30 to 48 inches) for larger Polygonum varieties.

Caring for Knotweed - Polygonum

Knotweed and other Polygonum plant genus members like to grow in a moist garden soil, so keep well watered.

The vine varieties of Polygonum should be pruned heavily at the start of spring to prevent scrawny growth and to make them more attractive.

Once flowering has finished, cut back the stems (usually in the autumn).

If you require more plants then they can be propagated by division in the autumn.

Common Questions

How many members does the Polygonum genus contain?

The Polygonum genus, commonly known as the Knotweeds, includes about 200-300 species.

Do Polygonum members make a good garden or landscaping plant?

Some Polygonum species can make good garden plants, but caution is required as many can become invasive due to their rapid growth.

Which Polygonum species are most frequently grown by gardeners?

Polygonum bistorta (Bistort) and Polygonum aubertii (Silverlace Vine) are occasionally grown, but with the awareness of their vigorous growth.

Are Polygonum plants fragrant?

Most Polygonum species are not particularly known for their fragrance.

What is the perfect location to grow Polygonum?

Polygonum is highly adaptable and can grow in a variety of conditions, from full sun to partial shade, and in different soil types.

Is Polygonum invasive in the USA, if so in which states?

Several Polygonum species, such as Polygonum cuspidatum (Japanese Knotweed), are currently considered invasive in many states in the USA.

How do I remove Polygonum plants from my garden?

Removing Polygonum can be challenging due to their robust root systems. Regularly cutting back and digging up roots is necessary to control their spread.

Summary

The Polygonum genus, commonly known as Knotweed, is part of the Buckwheat family, Polygonaceae. It includes annuals and perennials, with flowers ranging from white to pink.

These plants prefer full sun to partial shade and a variety of soil conditions. However, they are robust and can become invasive, so control measures may be necessary. They are best suited for naturalized areas or places where they can spread without restriction.

I hope that you enjoyed this guide on how to grow Polygonum plants. You may also enjoy the following Gardener's HQ growing guides: How to grow Sorrel and Rhubarb plants.